A common error in redacting information is to use an out-of-date or otherwise wrong method. Below is a partial list of methods NOT to use:

Changing the font to white

Turning the text white makes the words seem to disappear, but they don't. To see what can happen with this method, highlight (click & drag your mouse over) the sentence below. You will see the words are really there:
Mrs. Lincoln said that John Wilkes Booth shot her husband.

Blacking out with comment tools

Edits made by graphic and "commenting" tools which can black-out, cover over or remove sections of text can still be removed by anyone to reveal the text underneath. To see what can happen with this method, highlight (click & drag your mouse over) the sentence below. You will see the words are really there:

Mrs. Lincoln said that John Wilkes Booth shot her husband.

Deleting

Word-processing programs (such as Word or WordPerfect) retain embedded and hidden code called "metadata" containing revision history and other information. Metadata can reveal anything that was contained in the file at any time, even text that was previously deleted or changed, and even if the file was re-saved. Metadata are useful for tracking revisions, but if it is not purged from the document, anyone can view deleted information, even after the document has been converted to PDF.

Covering text with black marker, tape or paper

A scanned document redacted this way may still provide enough image detail to enable someone to see what was assumed hidden; this method should especially if that same data repeats a number of times across a document.

Cut-out (literally) all the text to be redacted and properly dispose of (shred) the clippings. This method will always be 100% effective.

Use opaque (100% impenetrable by light; neither transparent nor translucent) tape or paper to cover over the sections to be redacted. Do not use plain-paper as the scanner may pick up images through the paper. Even some black paper may allow some light reflection - so be careful.

Go through the document and mark all confidential words and/or phrases for redaction. You can mark for redaction by going to Tools→Mark for Redaction.

You will then need to create and save a copy of the newly redacted version in one of three formats: WordPerfect, Word, or PDF. After having done so, WordPerfect turns the redaction marks into opaque black bars.